Deflection coil system



1955 J. KAASHOEK ETAL 3,225,271

DEFLECTION COIL SYSTEM Filed July 2, 1963 2 Sheets-Sheet 1 INVENTORS JOHANNES KAASHOEK GERRIT J. LUBBEN AGA-Vvr 1965 J. KAASHOEK ETAL 3,225,271

DEFLECTION COIL SYSTEM Filed July 2, 1963 2 Sheets-Sheet 2 INVENTORS JOHANNES KAASHOEK GERRIT J LUBBEN United States Patet 3,225,271 DEFLECHON CQIL SYSTEM Johannes Kaashoek and Gerrit Jan Lubhen, Emmasingel, Eindhoven, Netherlands, assignors to North American Philips (Iompany, Inc, New York, N.Y., a corporation of Delaware Filed July 2, 1963, Ser. No. 292,232 Claims priority, application Netherlands, July 19, 1962, 281,181 4 Claims. (Cl. 317---200) This invention relates to deflection coil systems for the deflection of an electron ray in a cathode-ray tube, comprising at least two diametrically opposite halves of a coil which are wound in a tapered manner and the extent of taper of which is indicated by an angle i which varies in the longitudinal direction of the deflection coil system and which determines a magnitude h which is given by the formula:

3]4 cos I H R wherein H is a constant magnetic field strength on the axis of the deflection coil system, H is the value in amps. per cub. meter and varies in the longitudinal direction of the deflection coil system, and the magnitude h is positive at one end of the deflection coil system and negative at the other end thereof.

Such a deflection coil system is known from US. Letters Patent Nos. 2,866,125, 2,866,129, and 2,945,157, issued to J. Haantjes et al. As therein described the comically-wound halves of the coil are formed as aircore coils which may be slipped round the neck of a cathode-ray tube intended for the display of color television images. However, such air-core coils demand a larger number or longer windings for building up the electromagnetic filed required for deflection of the electron ray than does a coil which is wound on a core made of magnetic material such, for example, as ferroxcube. When using a core the ohmic value R of the coil thus becomes a minimum for a given inductance L, so that the losses i R, wherein i is the current traversing the coil, become minimum.

This is important especially for vertical deflection coils since for these coils substantially the ohmic value R has to be taken into account and regeneration of electromagnetic energy accumulated in the coils (as is the case in the horizontal deflection) is impossible.

It has therefore already been suggested in said patents to divide each half of the coil into four coils and to wind the first two on a first core and the other two on a second core of magnetic material. The taper was simulated in this case by choosing the radial angle made by two coils on a core to be different for the two coils on one core from that for the two coils on the other core.

The use of two cores has the disadvantage, however, that a certain space has to be reserved between the cores to accommodate the coils wound around a core. The deflection sensitivity is determined inter alia by the volume of the material employed for the cores. It will be evident that for a constant diameter of the circular cores, which diameter is substantially determined by the external diameter of the neck of the cathode-ray tube onto which the deflection coil system has to be slipped, and for a given angle of deflection of the electron ray the total length of the deflection coil system is greater with than without said interspace between the two cores.

In view of the tendency to make the necks of the tubes more and more narrow and short, especially in the case of the 'so-called index tubes for the display of colour television pictures in which only a single electron gun ice need be incorporated, it will be evident that the length of the deflection coil system must also be made as small as possible, while this system still has to fit around the neck of the tube as tightly as possible. A narrow neck is necessary for minimizing the deflection energy and in view of large angles of deflection it is necessary for a narrow neck to make the coil short, in order to permit the point of deflection (pivot of the electron beam on deflection) to be laid forward sutficiently far to prevent the formation of shadow (impact of electrons on the walls of the display tube).

This problem can be solved if, according to the invention, the two halves of the coil are mounted on a single core of magnetic material which is formed as a cylindrical support and the mean radius of which is equal to R cm., whilst I' is equal to half the mean radical angle made by one half of the coil.

As will be explained more fully hereinafter, said step is based on the recognition that, despite the use of a single core, the electromagnetic field active within the neck of the tube is not homogeneous, as could be expected, but inhomogeneous in the longitudinal direction of the deflection coil system if the halves of the coil are wound conically.

In addition to the advantage of the smaller length of the deflection coil system according to the invention, the structure of the assembly becomes much simpler, since instead of four coils on one core, hence in total eight coils on the two cores, for one direction of deflection it is now possible to wind one half of the coil on the cylindrical core in one continuous operation, thus rendering possible automatic winding of the two halves of the coil, which would be fairly difficult to realize with the eight individual coils.

Besides, it is now possible in a fairly simple manner to determine the taper by manufacturing the deflection coil system by a method which is characterized in that each half of the coil is wound in two packages each comprising a plurality of layers, the winding plane of one turn of a layer being at an angle to the axis of the core and said angle being the same, but opposite for the two packages.

By this method it is likewise possible to wind the coils for the vertical deflection in such a manner that during the horizontal flyback time the parasitic capacities between adjacent turns of sequential layers are charged to the least possible extent, so as to minimize the influence of the horizontal deflection on the vertical deflection.

in order to realize also the last-mentioned possibility, another method of manufacturing the deflection coil system is characterized in that each layer is wound in a direction going from the said plane through the axis of the core to a plane at right angles thereto, which also passes through the said axis, the wire being led back from the last turn of a layer of a first package to the first turn of the corresponding layer of the second package, and from the last turn of this layer of the second package to the first turn of the subsequent layer of the first package, and so forth.

In order that the invention may be readily carried into effect, one embodiment thereof will now be described in detail, by Way of example, with reference to the accompanying diagrammatic drawings, in which:

FIG. 1 shows one half of a coil wound on the cylindrical core, that is to say FIG. la is a side view, FIG. 1b an elevational view at the area z=z and FIG. 1c an elevational view at the area z=z FIG. 2 shows a cathode-ray tube having a deflecting system in accordance with the invention but shown for deflection in one direction only;

FIG. 3a is a cross-sectional view at the area 2 1 in FIG. 1, in which, to simplify the explanation, only four turns are shown;

FIG. 3b is a similar cross-sectional view at the area z=-z in FIG. 1;

FIG. 3c is a similar cross-sectional view at the area z=z in FIG. 1;

FIG. 4 shows diagrammatically in the unfolded state, a core with one half of the coil provided on it in two packages I and II, and

FIG. shows the core in the unfolded state to explain the method of winding by which the parasitic capacities between adjacent turns of sequential layers are maintained as favourable as possible.

FIG. 1a shows a cylindrical core 1 onto which one half 2 of the coil is wound. This half of the coil comprises two packages I and II each built up of several layers. Said figur'e also shows a system of co-ordinates comprising the axes x, y and z, the z-axis also being the axis of the tube onto which the coil system is slipped. The y-axis represents, for example, the vertical direction of deflection and the x-axis the horizontal direction of deflection. The point z=0 indicates the position of the electron gun which emits the electron ray, whilst the deflection coil system extends through a length of from z=-z to z=z the point z=z being aproximately midway between the point 2 and Z FIG. 1b is an elevational view of the deflection coil system at the area z=z and FIG. shows such an elevational view at the area z= z FIG. 2 shows a cathode ray tube having a single electron gun 26 for producing a single electron beam 27, which is deflected by means of the deflecting system in accordance with the invention and which comprises the core 1 and one half 2 of the coil wound on the core 1 for deflection in one direction. The coil for deflection in the other direction is not shown and can also be wound on core 1 or can be an air coil. In the latter case coil 2 may be for deflection in the vertical and the air coil for deflection in the horizontal direction.

Although in FIG. 2 there is shown a tube 25 with a single electron gun, the deflecting system in accordance with the invention may also be used for three gun color tube. In that case the three electron beams are deflected together by means of the single deflecting system.

From the total FIG. 1 it may be seen that the packages I and II engage each other as z=z and are somewhat spaced apart at Z='Z This is necessary because the electromagnetic field passing in a direction from 2 2 to z=-z is not allowed to be homogeneous, but must be inhomogeneous to prevent image faults, such as coma, astigmatismus and curvature of the image field. The extent of inhomogeneity is determined by the spacing between the packages I and II at z=z or, as explained in the preamble, by the extent of taper with which one half of the coil is wound on the core 1. Said extent of taper is determined by means of an angle I' the significance of which will be clarified with reference to FIG. 3. In fact, FIG. 3 shows cross-s'ections of the deflection coil system of FIG. 1 at z=z (FIG. 3a), at z=z (FIG.3b) and at 2: 2 (FIG. Each cross-section shows only four turns for the sake of simplicity. The turn formed by conductors 3 and 4 belongs, for example, to the package II and the turn formed by conductors 5 and 6 belongs to the package I. As previously mentioned in the preamble, each coil system comprises two halves of a coil, only one of which is shown in FIG. 1. The second half, which is wound on the other side of the core in entirely the same way as the half 2 of the coil, is shown diagrammatically in FIG. 3 by conductors 7, 8, 9 and 10 which form part of two packages in a corresponding manner as the conductors 3, 4, 5 and 6 form part of the packages II and I. In FIG. 311, lines 11 and 12 are drawn from the center of the figure to the conductors 3 and 5. The center corresponds to the z-axis of the core 1, which axis coincides in the operative position with the axis of the tube onto which the deflection coil system is slipped. The line 12 makes an angle P to the x-axis, so that the total angle made by the conductors 3 and 5, which belong to one half of the coil, is 2%,. In FIG. 3b, lines 13 and 4 are drawn from the center of the core 1 to the conductors 3 and 5. The line 13 is now at an angle I' to the x-axis, so that an angle 2%,, is made by the conductors 3 and 5 at z z At last, in FIG. 30, lines 15 and 16 are drawn, the line 15 being at an angle in, to the x-axis so that the conductors 3 and 5 make an angle 2 I' at z z In this embodiment the angle 1 thus increases in the direction from Z0 to z This radial angle I together with the magnitude R, being the mean radius of the core 1, which magnitude is indicated by the line 17 in FIG. 3, determine the magnitude h which is given by the formula:

wherein H is a constant magnetic field strength on the axis (directed along the y-axis in the example of FIG. 3) and H is the value in amps. per cub. metre which varies in the longitudinal direction of the deflection coil system.

In the embodiment chosen, 1 is smaller than 30 so that from the above-mentioned formula it follows that the magnitude h is positive at 1:2 Said magnitude is negative at z=z because the angle I is larger than 30. The angle I is about 30 so that the magnitude h is zero at z= z The magnitude It thus shows the desired variation, namely from positive to negative, as specified in said patents. It will be evident that for the other direction of deflection, the two other halves of the coil have to deliver a magnitude h which varies in exactly the opposite sense to the magnitude h just described, that is to say this magnitude must be negative at z=z and positive at z=z Besides, the absolute value of the magnitude h of the two halves of the coil must be greater at z=z for one direction of deflection than that for the other direction of deflection, from which it follows that the taper of the two halves of the coil must be different for one direction of deflection from that for the other direction of deflection.

The halves of the coil shown in FIG. 1 have to provide for the vertical deflection and the halves of the coil with opposite taper (and hence with opposite variation of the magnitude h) have to provide for the horizontal deflection, dependent upon the tube for which the deflection coils are intended.

Thus, for example, the deflection coil system shown in FIG. 1 can provide for the vertical deflection, for example in the case of an index tube in which the colour strips are positioned vertically, Whereas coils with an opposite taper provide for the horizontal deflection.

A preferred embodiment would be such that the coils for the vertical deflection are wound on the core 1, whereas the coils for the horizontal deflection are formed as air-core coils. The core 1 then fulfils the function of a support for the two deflection coil systems, considerably decreases the number of turns required for the vertical deflection coils and also decreases, though to a lesser extent, the number of turns of the coils for the horizontal direction of deflection.

When using the deflection coil system according to the invention for a Lawrence tube in which the colour strips are positioned horizontally, the taper is inverted, which implies that the vertical coils wound on the core must be manufactured in an exactly inverse manner to that shown in FIG. 1 and the taper of the horizontal coils has, of course, also to be matched correspondingly.

Not only the magnitudes P and R can be defined with FIG. 3, it being mentioned that the magnitude 1 is actually determined by the mean radial angle made by one pair of coil halves for a given value 2, but also the inhomogeneity of the field can be explained with FIG. 3. To this end, FIG. 3 shows the field lines which will occur when the conductors 3, 4, 5, 6, 7, 8, 9 and 10 are traversed by currents. For this variation of the field lines only the conductors 3, 5, 8 and 10 are important since the conductors 4, 6, 7 and 9 fulfil the function of return conductors. Crosses are drawn, for example, in the conductors 3 and 5, which indicates, as is wellknown, that the current enters in situ the plane of the drawing, whereas dots are drawn in the conductors 8 and 10, which indicates that the current leaves the plane of the drawing. The magnetic fields produced by said currents thus acquire directions as indicated by the arrow points in the field lines drawn around said conductors. The currents flow through the conductors 3 and 5 parallel with one another, as those in the conductors 8 and 10, but the currents in the conductors 3 and 5 are oppositely directed to those in the conductors 8 and 10. As is wellknown, the fields of parallel currents support one another whereas those of oppositely-directed currents counteract one another. The conductors 3 and 5, as the con ductors S and 10, are situated close to each other at zzz so the the fields produced by the conductors 3 and 5 have a tendency to close into a single field line as indicated, for example, by the field line 18 for the conductors 3 and 5 and by the field line 19 for the conductors 8 and 10. This closing into a single field line is enhanced by the material of the core 1 and if the currents flowing through the conductors 3 and 5 would not be opposite to those through the conductors 8 and 10, the field lines could close through the core and a magnetic field would not be active at all within the cylindrical core. However, it is the intention that such a field does occur within the core and because the currents flowing through the conductors 3 and 5 are opposite to those through the conductors 8 and 10, each field line is forced to pass over in the Y-direction so that a variation of field lines occurs within the core as shown in FIG. 3a, with the convex side of the curvature adjacent the y-axis.

Considering the situation at zzz it will be seen that the conductors 3 and 5, as the conductors 8 and 10, are spaced apart a greater distance. This implies that a field line will close more difiicultly around the conductors 3 and 5 and the conductors 8 and 10 respectively. This implies that the supporting action of parallel currents is decreased and the counteraction of oppositely-directed currents is increased. Since the supporting action in the case of FIG. 3a is enhanced by the material of the core, this will occur to a lesser extent in FIG. 3b. From this it follows that the field lines now pass over in the Y-direction substantially rectilinearly such, for example, as the field lines 20 and 21 in FIG. 311.

If the conductors 3 and 5, and the conductors 8 and 10 are spaced apart still further, as shown in FIG. 30, the supporting action of parallel currents, which is enhanced by the material of the core, will become manifest to an even smaller extent, but the counteracting effect of opposite currents will be increased still further. Consequently the field lines on passing over in the Y-direction will be curved in the opposite sense so that the concave side is adjacent the y-axis. This may clearly be seen from the field lines 22 and 23 in FIG. 3c. Thus in the Z-direction the desired inhomogeneity is obtained despite the fact that only a single core is used.

As already mentioned in the preamble, the process of winding the halves of the coil also becomes much simpler than in the case where four coils have to be wound on a core. This will be clarified with reference to FIGS. 4 and 5. For this purpose FIG. 4 shows the core 1 in the unfolded state and the conductors of the packages I and II are shown diagrammatically by lines which are at an angle to the line 24 which represents the plane passing through the axis of the core 1. The lines extend in a direction B B and A A respectively, for package I and in a direction C C and D D respectively, for package II. The winding process is as follows. The first layer of, for example, package I is wound starting at B and in a direction passing from B to A. When arrived at A the wire is led back from A to C for winding the first layer of package II in a direction passing from C to D. When arrived in D the wire is led back to B for winding the second layer of package I. This layer is also wound in a direction passing from B to A and, when arrived again at A the wire (see the second layer in FIG. 5) is led back to C for winding the second layer of package II in a direction from C to D. At last, the wire arrives at D and in FIG. 5 the winding process is not shown further. It will be evident, however, that from D the wire may be led back to B for winding the third layer of package I, and so forth. To fix the wires in position at B and C, either points of support may be provided on the core at B and C so that the wires cannot shift, or a templet may be placed on the core so that the wires cannot shift away from B and C. Such fixing is not necessary at B and C if the wires in situ engage one another. If the wires do not engage one another, for example, in view of a different angle I for obtaining a different variation of the magnitude H points of support must also be provided, or a trapezium-shaped templet must also be used at B and C When using thermo-adhesive wire the complete coil may be baked to form a compact assembly so that, if use is made of a templet, the wires cannot shift even if the templet is removed afterwards. A deflection coil having good symmetry properties may thus be obtained. Since there has always been wound in a direction from B to A, and in a direction from C to D and by throughconnecting from A to C, and from D to B, it is ensured that during operation the voltage induced in said conductors per layer from the other deflection coil has a polarity such that substantially no potential difference occurs between adjacent turns of sequential layers so that the parasitic capacities remain substantially uncharged. The camparatively great difference in potential between the turns of package I at B and those of package II at C has no detrimental influence because the capacity is very low due to the comparatively large mean distance between said turns. Especially if the deflection coil system for the horizontal deflection is formed as an air-core coil, the above-described winding method affords the advantage that the voltage induced in the vertical deflection coils during the horizontal fly-back time has substantially no influence on the vertical deflection.

The deflection coil system described may be used not only for a colour television display tube of the indextype or of the Lawrence type, but also for a colour display tube having three electron guns as described, for example in US. Letters Patent 2,945,157. The deflection coils can also succesfully be used, however, for a black-and-white display tube since in such a display tube the image faults can also be reduced to a minimum by said coils. Since a spot is thus obtained which is more or less elliptic it is possible to eliminate the line structure if the long axis of the ellipse is placed in the vertical direction. Such is the case if the taper for the vertical deflection coils varies as shown in FIG. 1 and the taper for the horizontal deflection coils varies in the opposite sense.

What is claimed is:

1. A deflection coil system for deflecting an electron ray about a longitudinal axis in a cathode ray tube, comprising a cylindrical core of magnetic material encircling the said axis, a toroidal winding on said core comprising two winding sections spaced apart in diametrical confronting relationship, each of said sections comprising two coils adjacently arranged and having current flow in the same direction, said winding producing a deflection field having an intensity 1i 3+4= cos I' H() R2 where H, is the magnteic field strength in the axis of the deflection coil system, H is the value in amperes per cubic meter of the winding, I is half the acute angle between said adjacently arranged coils, and R is the mean radius of the winding in cm., the coils of each of said sections being separated by a varying amount along the longitudinal axis thereby to vary the said angle 1' in the longitudinal direction and produce variations of the said value h along the said longitudinal direction whereby h has a positive value at one end of the deflection system and a negative value at the other end thereof.

2. A deflection coil system for deflecting an electron ray about a longitudinal axis in a cathode ray tube, comprising a cylindrical core of magnetic material encircling the said axis, a toroidal winding on said core comprising two winding sections spaced apart in diametrical confronting relationship, each of said sections comprising two coils adjacently arranged and having current flow in the same direction, said winding producing a deflection field having an intensity 3+4 cos 1 H R where H is the magnetic field strength in the axis of the deflection coil system, H is the value in amperes per cubic meter of the winding, I is half the acute angle between said adjacently arranged coils, and R is the mean radius of the winding in cm., the coils of each of said sections being separated by an amount increasing along the longitudinal axis in the direction of travel of the electron ray thereby to vary the said angle I in the longitudinal direction and produce variations of the said value h along the said longitudinal direction whereby h has a positive value at the entrance end of the deflection system and a negative value at the exit end thereof.

3. A deflection coil system for deflecting an electron ray about a longitudinal axis in a cathode ray tube, comprising a cylindrical core of magnetic material encircling the said axis, a toroidal winding on said core comprising two winding sections spaced apart in diametrical confronting relationship, each of said sections comprising two coils adjacently arranged and having current flow in the same direction, said winding producing a deflection field having an intensity where H, is the magnetic field strength in the axis of the deflection coil system, H is the value in amperes per cubic -8 said adjacently arranged coils, and R is the mean radius of. the winding in cm., the coils of each of said sections being substantially in contact at the entrance end of the deflection system and being separated by a varying amount 'along the longitudinal axis towards the exit end of the deflection system thereby to vary the said angle 1 in the longitudinal direction and produce variations of the said value h along the said longitudinal direction whereby h has a positive value at the said entrance end and a negative value at the exit end. 7

4. A deflection coil system for deflecting an electron ray about a longitudinal axis in a cathode ray tube, comprising a cylindrical core of magnetic material encircling the said axis, a toroidal winding on said core comprising two winding sections spaced apart in diametrical confronting rela tionship, each of said sections comprising two coils adjacently arranged and having current flow in the same direction, said winding producing a deflection field having an intensity where H, is the magnetic field strength in the axis of the deflection coil system, H is the value in amperes per cubic meter of the winding, and I is half the acute angle between said adjacently arranged coils, and R is the mean radius of the winding in cm., the coils of each of said sections being separated by a varying amount along the longitudinal axis, thereby to vary the said angle I in the longitudinal direction and produce variations of the said value h along the said longitudinal direction whereby h has a positive value atone end of the deflection system and a negative value at the other end thereof, said coils having multiple layers and the layers of adjacent coils being wound consecutively with alternately arranged turns whereby the outer turn of a layer of one coil directly leads to the inner turn of the adjacently disposed layer of the other coil.

References Qited by the Examiner UNITED STATES PATENTS 2,455,171 11/1948 Haantjes 3l375 2,945,157 7/1960 Haantjes 313-76 3,115,544 12/1963 Marley 3l376 BERNARD A. GILHEANY, Primary Examiner.

JOHN F. BURNS, Examiner. 

1. A DEFLECTION COIL SYSTEM FOR DEFLECTING AN ELECTRON RAY ABOUT A LONGITUDINAL AXIS IN A CATHODE RAY TUBE, COMPRISING A CYLINDRICAL CORE OF MAGNETIC MATERIAL ENCIRCLING THE SAID AXIS, A TOROIDAL WINDING ON SAID CORE COMPRISNG TWO WINDING SECTIONS SPACED APART IN A DIAMETRICAL CONFRONTING RELATIONSHIP, EACH OF SAID SECTIONS COMPRISING TWO COILS ADJACENTLY ARRANGED AND HAVING CURRENT FLOW IN THE SAME DIRECTION, SAID WINDING PRODUCING A DEFLECTION FIELD HAVING AN INTENSITY 